My invention pertains to transfer apparatus for energy sources. More specifically, the invention relates to apparatus which automatically transfers to a standby energy source if the main or principal source fails to supply energy to the associated load circuitry.
In some types of electrical installations, it is extremely important to have continuity of service even though failures in parts of the apparatus may occur. For example, the reliability of railroad track circuits is a critical factor, particularly in interlocking areas where a track circuit failure will lock out the involved interlocking routes. If the track circuit is of the audio frequency (AF) type so that a transmitter unit having a selected frequency is the source of energy for track circuit operation, failure of this transmitter will cause the track circuit to fail, that is, to indicate an occupied condition, and thus lock out the signaling system involved. It is, of course, possible to provide a standby transmitter for such critical track circuits. However, the peculiar characteristics of a track circuit between its unoccupied and occupied conditions, that is, between a very light load and an extremely heavy load requirement, make automatic changeover control more difficult than with simpler fixed load arrangements. The transfer apparatus must distinguish between the required output for the transmitter between the two load conditions to assure that changeover to the standby occurs only if the principal transmitter has actually failed and is providing no output at all. A similar situation will exist where a special type of energy source is providing operating energy to a load circuit or network in which an extreme variation occurs between the light or no load and the full load conditions. Accordingly, an object of my invention is a circuit arrangement for automatically transferring from a main to a standby energy source for supplying a variable load network.
Another object of the invention is transfer apparatus for shifting from a main to a standby energy source for a track circuit.
A further object of my invention is appartus for audio frequency track circuits to transfer from the principal transmitter energy source to a standby transmitter source if the principal source is detected as having failed under either unloaded or loaded conditions within the track circuit.
Still another object of the invention is apparatus for shifting automatically to a standby energy source if the output of a main or principal source is detected as having failed under either loaded or unloaded conditions in the circuit network.
Also an object of my invention is an energy source transfer circuit arrangement having first and second detection or monitoring channels for checking the output from the energy source whether it is supplying a loaded or unloaded circuit network and for shifting to an alternate energy source if no output is detected under either load condition.
A still further object of the invention is transfer apparatus for shifting from a main transmitter to an alternate or standby transmitter to supply energy to an audio frequency track circuit, the transfer apparatus including two output detection channels, one responsive to a no-load output condition when the track circuit is unoccupied and the other responsive to a loaded output condition when the track is occupied, the presence of at least one of the two detection signals being required to hold the main transmitter in service.
Other objects, features, and advantages of my invention will become apparent from the following specification and appended claims when taken with the accompanying drawings.